1. Field of the Invention
The present invention relates to a liquid crystal composition, a polymer, a film, and a cholesteric liquid crystal.
2. Background Art
An optically active compound (hereinafter, also referred to as a chiral agent) induces a helical twist in a liquid crystal or can be used as a dopant strengthening the helical twist.
Here, as an index indicating the performance of a chiral agent, HTP is generally used. HTP is an abbreviation for Helical Twisting Power and is a factor for indicating helical alignment ability represented by the following formula (1). Specifically, the description thereof is included in “Development of Light Reactive Chiral Agent for Cholesteric Liquid Crystal for Color Filter Used for Liquid Crystal Display” (Fujifilm Research & Development, No. 50, pp. 60 to 63, Masatoshi YUMOTO and Mitsuyoshi ICHIHASHI).HTP=Refractive index of liquid crystal/(reflection wavelength×concentration of chiral agent)  Formula (1)
As an application example of a liquid crystal using a chiral agent, an infrared reflective film obtained by laminating a specific phase difference film using, for example, a cholesteric liquid crystal phase and a reflective circular polarizing plate is known. In order to prepare a light reflective film with high performance, it is necessary to reduce haze of a film and to control a reflection wavelength bandwidth with high precision.
For example, a method of adding a chiral agent to a liquid crystal compound (for example, a rod-like liquid crystal compound) showing a cholesteric liquid crystal phase, adjusting the additive concentration of the chiral agent, and adjusting a reflection bandwidth is generally used for reflecting light having a long wavelength in an infrared light region. In this case, qualitatively, it is necessary to reduce the amount of the chiral agent to be added for shifting the reflection wavelength to the long wavelength side. Next, the alignment of the cholesteric liquid crystal phase needs to be improved for reducing the haze of the film. In this manner, alignment defects of the light reflective film can be eliminated and the haze thereof can be lowered. Accordingly, it is desired that the reflection wavelength be adjusted by using a small amount of the chiral agent with high HTP to be added, in order to shift the reflection wavelength to the long wavelength side such that infrared light is reflected and to prepare the light reflective film with excellent alignment.
As the optically active compound, various chiral agents are known (for example, described in “Liquid Crystal Device Handbook,” chapter 3, paragraph 4-3, TN, chiral agent for STN, pp. 199, edited by 142nd Committee of Japan Society for Promotion of Science, in 1989). The optically active compound generally contains asymmetric carbon atoms, an axially asymmetric compound not containing asymmetric carbon atoms or a planarly asymmetric compound can be used as a chiral agent. As an example of the axially asymmetric compound or a planarly asymmetric compound, binaphthol or a derivative thereof is known. For example, Patent Document 1 discloses an example of a liquid crystal mixture using sulfuric acid ester of binaphthol which is made into a derivative as a chiral agent.
Also, as other compounds having a binaphthol skeleton, Non-Patent Document 1 discloses a synthetic method of an asymmetric catalyst and an example of using binaphthol sulfurous ester as a synthetic intermediate. However, in Non-Patent Document 1, the example of using binaphthol sulfurous ester as a chiral agent is not disclosed and application of a liquid crystal compound as a chiral agent is not described.